As previously mentioned, many words that we use in our everyday speech assume a more precise and often restricted meaning in the language of science. The words "work", "energy", and "power" considered in this article are quite familiar to everyone; nevertheless, their use in scientific terminology presents certain difficulties. Discussing these three terms in some detail is the subject of our present article for we know of their being often misused.

The word "work" may serve as an example. Besides its being an English word in common usage, it is also a scientific term which has a special meaning when used in mechanics.

When we are standing and holding a heavy weight, when we are studying or teaching at the institute — we say that we are working. Studying may be very hard. We know that it will make you tired at times; nevertheless, no physicist will ever call it work. The scientific term "work" is much more restricted. Mechanical work is performed only when a force moves some object through a distance.

One can perform work by lifting a box from the floor. Pushing the box along the floor against friction also means doing work. According to physical laws you cannot perform any work, scientifically speaking, by pushing an automobile which is standing on the road, unless it starts moving. Thus, in order to do mechanical work two conditions are necessary, namely, there must be a force and it must act through a distance. Generally speaking, the greater the force and the distance moved, the greater the work performed.

Work and energy are very closely related. Indeed, one may say that the energy of a body or system is the capacity of that system or body for doing work. Power is related to both work and energy. It is the rate of performing the work in a unit of time.

While energy is the capacity for work, power is the quantity of work done in a unit of time. When a kilogram is lifted to a height of one meter, we say that a kilogram-meter of work is accomplished. The amount of the accomplished work does not depend on the time spent on lifting this weight.

Considering power requires considering the rate of performing the work. For example, if a weight is lifted to a height of one meter in one second, twice as much power will be required than in case that very weight were lifted to a height of one meter in two seconds.

If someone carried a 15-kg box up the stairs in 10 sec, the staircase being 6 m high, he would work at the average rate of 90 kgm divided by 10 sec, or 9 kgm per second.

Measuring power, we generally use such units as watts, kilowatts, and kilogram-meters per second. Seventy five kg. m. s. (kilogram-meters per second) or 736 W (watts) form a horse-power. A horse-power is a unit for measuring the amount of work performed per second.

Discussing the term "energy", we shall follow the transformation of one form of energy into another.